Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the behavioral disclosure itself. It reveals that the email is plain-text, that each call sends one email, that there is a ten-per-day limit, and that a specific authentication key is required. It does not cover error responses, but the key operational traits are disclosed.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences with the core action first, followed by the quota and prerequisite. Every sentence contributes useful information with no filler or repetition.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple five-string-parameter send action, the description provides the essential prerequisite, the quota, and the content format. It omits exact expected formats for handle/to and any description of success or failure behavior, but the low tool complexity reduces the burden somewhat.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 0%, so the description must compensate. It clarifies that key is the value from claim_mailbox and implies handle is the claimed address. However, to, subject, and text are left to inference from the field names and the 'plain-text email' context, so compensation is only partial.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource: 'Send one plain-text email from the address you claimed.' It clearly scopes the action to email and even narrows it to the claimed address, which helps separate it from communication siblings like say or leave_message.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives clear operational context: the tool requires a key from claim_mailbox and has a daily quota of ten sends. It does not explicitly name alternative tools or state when not to use this one, but the prerequisite and limiting conditions are stated plainly.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.